Display system and image reproduction device

ABSTRACT

Image reproduction devices ( 10   a  to  10   e ) and a management device ( 20 ) each hold moving image data. The management device ( 20 ) goes into a reproduction standby state in which the moving image data ( 50 ) can be reproduced and instructs the image reproduction devices ( 10   a  to  10   e ) to go into the reproduction standby state, by cascade communication. The management device ( 20 ) starts reproduction of the moving image data ( 50 ) and instructs the image reproduction devices ( 10   a  to  10   e ) to start reproduction of the moving image data ( 50 ), by broadcast communication. The management device ( 20 ) periodically broadcasts synchronization information ( 252 ). The image reproduction devices ( 10   a  to  10   e ) use the synchronization information ( 252 ) to specify a frame number of a frame displayed on the management device ( 20 ). Frames corresponding to the specified frame number are displayed on the display parts ( 110   a  to  110   e ).

TECHNICAL FIELD

The present invention relates to a display system constituted of thindisplay devices each using liquid crystal display panels or the like.

BACKGROUND ART

In retail stores such as supermarkets, convenience stores, and the like,generally, display racks are placed in the stores and commercial goodsare displayed on the display racks. Further, for the purpose of salespromotion of the goods displayed on the display racks, a techniquecalled “electronic POP (Point Of Purchase)” has been conventionallyused.

[Patent Document 1] Japanese Patent Application Laid Open Gazette No.2001-100683

[Patent Document 2] Japanese Patent Application Laid Open Gazette No.2007-289636

Patent Document 1 discloses an electronic POP apparatus using a thindisplay panel such as a liquid crystal display panel or the like. In theelectronic POP apparatus disclosed in Patent Document 1, an advertisingvideo image is displayed on the liquid crystal display panel or the likeby reproducing moving image data or the like stored in a storage medium.For using the electronic POP apparatus of Patent Document 1, however,another space for setting the electronic POP apparatus is neededseparately from the space for displaying the commercial goods.

Patent Document 2 discloses a display rack on which a video image forelectronic POP can be displayed. A projector is set inside the displayrack and a transmission screen is attached to a front surface of a shelfboard on which the commercial goods are placed. An advertising videoimage is displayed entirely on the display rack by displaying theadvertising video image projected from the projector on the screen. Thedisplay rack of Patent Document 2 allows display of the advertisingvideo image thereon, not requiring any space for setting an electronicPOP apparatus, and it is thereby possible to efficiently use thesalesrooms in the retail stores.

Electronic POP systems in each of which one video image is displayed ona plurality of display devices have been also used. In order tosynchronize video images displayed on the display devices, such anelectronic POP system needs a content reproduction device for generatingframes to be displayed on the display devices, respectively, from movingimage data and distributing the frames to the display devices.Therefore, the electronic POP system using a plurality of displaydevices disadvantageously has a complicated configuration, and thisarises a problem that it is difficult to lower the price thereof.

DISCLOSURE OF INVENTION

The present invention is intended for a display system. According to thepresent invention, the display system includes a first imagereproduction device for reproducing first moving image data and a secondimage reproduction device for reproducing second moving image data,which can be communicated with the first image reproduction device, andin the display system of the present invention, the first imagereproduction device and the second image reproduction device eachcomprise a storage part for storing therein moving image data to bereproduced by the device itself, a decoder for decoding the moving imagedata stored in the storage part, to thereby generate a frame, and adisplay part for displaying the frame thereon in the order of framenumber, the second image reproduction device further comprises asynchronization information transmitting part for transmittingsynchronization information including information specifying a framenumber of a reference frame displayed on the display part of the secondimage reproduction device to the first image reproduction device byunidirectional communication, and the first image reproduction devicefurther comprises a frame adjustment part for specifying the framenumber of the reference frame on the basis of the synchronizationinformation and displaying a frame corresponding to the frame numberspecified thus on the display part.

The display system needs no device other than the first imagereproduction device and the second image reproduction device and cansynchronize the frame numbers of the pieces of moving image datareproduced by these devices, respectively. Therefore, it is possible tosimplify the configuration of the display system.

According to another preferred embodiment, the display system furtherincludes a third image reproduction device for reproducing third movingimage data, and in the display system of another preferred embodiment,the synchronization information transmitting part (251) includes abroadcast communication part for broadcasting the synchronizationinformation to the first image reproduction device and the third imagereproduction device by unidirectional communication.

It is thereby possible to easily synchronize the pieces of moving imagedata reproduced by three or more image reproduction devices.

Therefore, it is an object of the present invention to provide atechnique for facilitating reduction in the cost of a display systemwhich displays one video image by using a plurality of display devices.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] is a schematic diagram showing a configuration of a displaysystem in accordance with a preferred embodiment of the presentinvention;

[FIG. 2] is a perspective view of an image reproduction device;

[FIG. 3] is a view showing an exemplary state where the imagereproduction devices and a management device are attached;

[FIG. 4A] is a view showing moving image data used for displaying avideo image on the whole of the display system;

[FIG. 4B] is a view showing a state where the pieces of moving imagedata are reproduced out of synchronization;

[FIG. 4C] is a view showing a state where the pieces of moving imagedata are reproduced in synchronization;

[FIG. 5] is a block diagram showing a functional constitution of theimage reproduction device;

[FIG. 6] is a block diagram showing a functional constitution of themanagement device;

[FIG. 7] is a flowchart showing an operation flow for distributingmoving image data;

[FIG. 8] is a view showing distribution destination information;

[FIG. 9] is a view showing a cascade communication packet;

[FIG. 10] is a view showing a broadcast communication packet;

[FIG. 11] is a flowchart showing an operation flow for adjusting a frameto be displayed on a display part by using synchronization information;and

[FIG. 12] is a schematic diagram showing another exemplary configurationof the display system.

BEST MODE FOR CARRYING OUT THE INVENTION

{Configuration and Use of Display System}

Hereinafter, with reference to figures, the preferred embodiment of thepresent invention will be discussed. FIG. 1 is a schematic diagramshowing a display system 1 in accordance with the preferred embodiment.The display system 1 comprises image reproduction devices 10 a, 10 b, 10c, 10 d, and 10 e, a management device 20, and a communication cable 30.The image reproduction devices 10 a to 10 e and the management device 20each have a function for reproducing moving image data 50.

The display system 1 can be used as an electronic POP system and candisplay one video image by using the image reproduction devices 10 a to10 e and the management device 20. In this case, The pieces of movingimage data 50 held by the image reproduction devices 10 a to 10 e andthe management device 20 are obtained by dividing one piece of movingimage data 500 (see FIG. 4A) by six. In order for these devices toreproduce the pieces of moving image data 50 in synchronization, themanagement device 20 periodically sends synchronization information 252to the image reproduction devices 10 a to 10 e.

The image reproduction devices 10 a to 10 e have display parts 110 a to110 e, respectively, and the display parts 110 a to 110 e are eachconstituted of liquid crystal display panels 11, 11, and 11. In each ofthe display parts 110 a to 110 e, the three liquid crystal displaypanels 11 are aligned in a horizontal scan direction and constitute onevirtual display panel. In other words, the three liquid crystal displaypanels 11 displays thereon a reproduced video image of the moving imagedata 50 on the whole.

The image reproduction devices 10 a to 10 e have the same configuration.For this reason, when common discussion on the image reproductiondevices 10 a to 10 e will be made, the image reproduction devices aregenerally referred to as the image reproduction device(s) 10, notindividually referred to as the image reproduction devices 10 a, 10 b, .. . , and 10 e.

The management device 20 also has a function for managing the imagereproduction devices 10 as well as the function for reproducing themoving image data 50. Specifically, the management device 20 performsdistribution of the moving image data 50 to the image reproductiondevices 10, gives an instruction for reproduction of the moving imagedata 50 to the image reproduction devices 10, and so on. The managementdevice 20 has a display part 210 constituted of three liquid crystaldisplay panels 21, like the image reproduction devices 10.

The communication cable 30 is a cable which accommodates a standard suchas RS-485 or the like and connects the image reproduction devices 10 andthe management device 20 to each other.

{Appearance of Image Reproduction Device 10}

FIG. 2 is a perspective view of the image reproduction device 10. Theimage reproduction device 10 further comprises a housing 12, anattachment part 13, and a tilt control part 14 as well as the threeliquid crystal display panels 11. The appearance of the managementdevice 20 is the same as that of the image reproduction device 10,except that the management device 20 further comprises a memory cardslot 26 (see FIG. 6).

The housing 12 accommodates a control part 15 (see FIG. 5) of the imagereproduction device 10 and fixes the three liquid crystal display panels11 on the same plane. The attachment part 13 fixes the imagereproduction device 10. The tilt control part 14 controls theorientation of a display surface of the liquid crystal display panel 11.

{Attachment of Image Reproduction Devices 10 and Management Device 20}

FIG. 3 is a view showing an exemplary use of the display system 1. Theimage reproduction devices 10 and the management device 20 are attachedto front surfaces of shelf boards 41 of a display rack 4 which is usedfor display of commercial goods. On the upper shelf board 41, themanagement device 20, the image reproduction device 10 a, and the imagereproduction device 10 b are attached in this order from the backthereof On the lower shelf board 41, the image reproduction devices 10c, 10 d, and 10 e are attached in this order from the back thereofInside a wiring cover 42 which is attached to a lower surface of eachshelf board 41, accommodated are the communication cable 30 and a powerline for supplying power to the image reproduction devices 10 and themanagement device 20.

By attaching the image reproduction devices 10 and the management device20 to the display rack 4, an advertising video image of commercial goodsis displayed on the whole of the display rack 4. As shown in FIG. 3, byusing the tilt control part 14, the orientations of the display parts ofthe image reproduction devices 10 and the management device 20 can becontrolled to be so angled as to be easily viewed by customers. Thedisplay system 1 attached to the display rack 4 can thereby display aclear video image and this increases the effect of sales promotion.

In order to suit to a limited space such as the front surface of theshelf board 41 or the like, the image reproduction devices 10 and themanagement device 20 have elongated display parts 110 and 210 eachconstituted of a plurality of liquid crystal display panels 11.Therefore, since the display system 1 does not need to use any liquidcrystal display panel suited to the size of the front surface of theshelf board 41, it is thereby possible to achieve substantial reductionin the cost.

{Overview of Reproduction of Moving Image Data 50}

Next, an overview of reproduction of the moving image data 50 will bediscussed. As content data to be used for display of one video image onthe whole of the display system 1, moving image data 500 is generated.The moving image data 500 is divided into six pieces of moving imagedata 50 in accordance with display areas of the image reproductiondevices 10 and the management device 20.

FIG. 4A is a view showing a frame 500 a of the moving image data 500.The frame 500 a shown in FIG. 4A corresponds to a frame number 128, inwhich circles 501 and 501 are drawn. The circles 501 and 501 are movedfrom the left side to the right side of the paper as the reproductionproceeds.

By dividing the frame 500 a into the six areas, six pieces of movingimage data 50 are generated. The management device 20, the imagereproduction device 10 a, and the image reproduction device 10 bcorrespond to the left side area, the center area, and the right sidearea on the upper row of the frame 500 a, respectively. The imagereproduction device 10 c, the image reproduction device 10 d and theimage reproduction device 10 e correspond to the left side area, thecenter area, and the right side area on the lower row of the frame 500a, respectively. The image reproduction devices 10 and the managementdevice 20 hold the pieces of moving image data 50 corresponding to therespective areas.

The image reproduction devices 10 and the management device 20 decodethe respective pieces of moving image data 50, to thereby generate theframes, and display the frames in the order of the frame number. Eachframe is updated at a frequency of 30 frames or the like per second onthe basis of a clock signal generated by a crystal oscillator includedin each of the devices. Since the characteristics of the crystaloscillators included in the devices vary, however, the timings forupdating the frame in the devices are not completely coincident.

Immediately after the reproductions of the moving image data 50 in theimage reproduction devices 10 and the management device 20 are startedat the same time, the difference in the timing for updating the frameamong the devices is very small, e.g., about a few milliseconds. As thereproductions of the moving image data 50 proceed, the difference in theupdate timing becomes larger. As a result, there occurs a differenceamong the frame numbers of the frames displayed on these devices.

FIG. 4B is a view showing the moving image data 500 displayed on thewhole of the display rack 4 with the difference in the frame number.When there occurs a difference among the frame numbers of the framesdisplayed on the devices, the frames in which the respective positionsof the circles 501 are different are displayed on the display parts 110a to 110 e and 210. As a result, the video image displayed on the wholeof the display rack 4 lacks a sense of unity.

Then, the management device 20 periodically sends the synchronizationinformation 252 to the image reproduction devices 10 a to 10 e. Thesynchronization information 252 includes information specifying a framenumber of a frame displayed on the management device 20 and a time stampindicating the display time of the frame. On the basis of thesynchronization information 252, each of the image reproduction devices10 synchronizes a frame number of a frame displayed on the display part110 thereof with the frame number specified by using the synchronizationinformation 252. The image reproduction devices 10 and the managementdevice 20 can thereby display the frames of the same frame number, asshown in FIG. 4C. Therefore, the display system 1 can display a unifiedvideo image on the whole of the display rack 4.

{Functional Constitution of Image Reproduction Device 10}

FIG. 5 is a block diagram showing a functional constitution of the imagereproduction device 10. The image reproduction device 10 comprises acontrol part 15, a panel control part 16, a storage part 17, and acommunication control part 18 as well as the display part 110.

The control part 15 performs a general control of the image reproductiondevice 10. The control part 15 comprises a decoder 151, a clockgeneration circuit 152, a cumulative counter part 153, and a frameadjustment part 154.

The decoder 151 decodes the moving image data 50 stored in the storagepart 17, to thereby generate a frame. The clock generation circuit 152incorporates a crystal oscillator (not shown) to generate a clocksignal. The cumulative counter part 153 cumulatively counts the clocksignal from the time when the image reproduction device 10 startsreproduction of the moving image data 50.

The frame adjustment part 154 uses cumulative count information 155 andthe synchronization information 252 received from the management device20 to specify a frame number of a frame displayed on the managementdevice 20. The cumulative count information 155 is information in whicha cumulative count value obtained by the cumulative counter part 153 isrecorded. The panel control part 16 is notified of the frame numberwhich is specified by the frame adjustment part 154.

The panel control part 16 counts the clock signal and updates the frameto be displayed on the display part 110 every time when the count valueof the clock signal reaches an update count value. In a normal state,the frame is displayed on the display part 110 in the order of the framenumber. When the frame adjustment part 154 notifies the panel controlpart 16 of the frame number, the panel control part 16 displays a framecorresponding to the notified frame number on the display part 110.

The storage part 17 is a flash memory or the like and stores the movingimage data 50 therein. The communication control part 18 performs serialcommunication on the basis of the standard of RS-485.

{Functional Constitution of Management Device 20}

FIG. 6 is a block diagram showing a functional constitution of themanagement device 20. Constituent elements identical to those of theimage reproduction device 10 are represented by the same reference signsand discussion thereof will be omitted.

The management device 20 further comprises the panel control part 16,the storage part 17, the communication control part 18, a control part25, and a memory card slot 26 as well as the display part 210.

The control part 25 performs a general control of the management device20. The control part 25 comprises the decoder 151, the clock generationcircuit 152, the cumulative counter part 153, and a synchronizationinformation transmitting part 251.

The synchronization information transmitting part 251 periodicallygenerates the synchronization information 252 and broadcasts thesynchronization information 252 to the image reproduction devices 10.The synchronization information transmitting part 251 holds thecumulative count value at the last frame update as reference countinformation 253. The synchronization information 252 includes thereference count information 253 and a time stamp indicating the lastframe update time.

Into the memory card slot 26, a memory card 45 is inserted. In thememory card 45, the pieces of moving image data 50, 50, . . . anddistribution destination information 46 are stored. The number of movingimage data 50 to be stored in the memory card 45 corresponds to thenumber of the image reproduction devices 10 and the management device 20(i.e., six). The distribution destination information 46 is informationassociating each moving image data 50 with the (destination) device towhich the moving image data 50 is distributed.

{Operation of Display System 1}

Hereinafter, as to operations of the display system 1, (1) communicationmodes used in the display system 1, (2) distribution of the moving imagedata 50, (3) start of reproduction of the moving image data 50, and (4)display of the moving image data 50 in synchronization will be discussedin this order.

(1) Communication Modes used in Display System

The management device 20 performs distribution of the moving image data50, gives an instruction for starting reproduction of the moving imagedata 50, and sends the synchronization information 252 to the imagereproduction devices 10. For efficient communication with the imagereproduction devices 10, the management device 20 performs eithercascade communication or broadcast communication depending on thepurpose of communication.

The cascade communication is bidirectional communication between themanagement device 20 and each of the image reproduction devices 10. Thecascade communication is used when the management device 20 distributesthe moving image data 50 having a large data size. The cascadecommunication is used also when the management device 20 requires theimage reproduction device 10 to transmit status information thereto. Inother words, the cascade communication is one-to-one communication, andtherefore, the management device 20 cannot simultaneously transmit datato a plurality of image reproduction devices 10.

The broadcast communication is unidirectional communication from themanagement device 20 to the image reproduction devices 10 and used whenthe management device 20 transmits data to all the image reproductiondevices 10 at the same time. In other words, the broadcast communicationis used when the management device 20 controls the operation timing ofall the image reproduction devices 10. As exemplary cases forcontrolling the operation timing, there are cases where the managementdevice 20 gives an instruction for starting reproduction to all theimage reproduction devices 10 and where the management device 20 sendsthe synchronization information 252 to all the image reproductiondevices 10.

The cascade communication and the broadcast communication are performedvia the communication cable 30. For this reason, the management device20 performs time sharing control of the cascade communication and thebroadcast communication in order to prevent communications from beingperformed by the two communication modes at the same time.

(2) Distribution of Moving Image Data 50

The management device 20 distributes the moving image data 50 stored inthe memory card 45 to one of the image reproduction devices 10 on thebasis of the distribution destination information 46. It is therebypossible to simplify the operation of storing the moving image data 50in each of these devices.

FIG. 7 is a flowchart showing an operation flow of the management device20 for distributing the moving image data 50. As an initial state, nomoving image data 50 is stored in the storage part 17 of each of theimage reproduction devices 10 and the management device 20.

The management device 20 starts the operation shown in the flowchart ofFIG. 7 when the memory card 45 is inserted into the memory card slot 26.The management device 20 specifies a distribution destination of themoving image data 50 stored in the memory card 45 on the basis of thedistribution destination information 46 (Step S11). FIG. 8 is a viewshowing an example of distribution destination information 46. Forexample, a file name “fileA.mpg” is associated with identifyinginformation “10 a” of the image reproduction device 10 a. The respectiveidentifying information of the image reproduction devices 10 b to 10 eare “10 b” to “10 e” and the identifying information of the managementdevice 20 is “20”. The management device 20 specifies the imagereproduction device 10 a as the distribution destination of the movingimage data 50 having a file name “fileA.mpg”.

In order to transmit the moving image data 50 with the file name“fileA.mpg” to the image reproduction device 10 a, the management device20 generates a cascade communication packet 55 (Step S12).

FIG. 9 is a view showing an exemplary communication packet 55. Thecommunication packet 55 shown in FIG. 9 is a communication packet whichis generated for distribution of the moving image data 50 with the filename “fileA.mpg”. The communication packet 55 is constituted of adetection/synchronization code part 51, a destination address part 52, apayload part 53, and an error code part 54.

In the detection/synchronization code part 51, stored is codeinformation used when the receiving-side image reproduction device 10 adetects the communication packet 55. In the destination address part 52,set is the identifying information “10 a” of the destination of thecommunication packet 55, i.e., the image reproduction device 10 a. Inthe payload part 53, stored is the moving image data 50 to bedistributed. Further, in the payload part 53, a control command for theimage reproduction device 10, status information of the device, and thelike can be stored, as well as the moving image data 50. In the errorcode part 54, stored is an error detection code used for detecting anerror of the communication packet 55.

The management device 20 confirms that the communication packet 55 canbe sent out (“Yes” in Step S13) and transmits the communication packet55 to the image reproduction device 10 a (Step S14). As a case where thecommunication packet 55 cannot be sent out, there is a case where thetime slot is assigned to the broadcast communication, or the like. Inthis case, the management device 20 waits until the cascadecommunication can be performed and thereafter performs an operation ofStep S14.

When the image reproduction device 10 a receives the communicationpacket 55 shown in FIG. 9, the image reproduction device 10 a stores themoving image data 50 stored in the communication packet 55 into thestorage part 17. The image reproduction device 10 a transmits a responseto the communication packet 55 to the management device 20 by cascadecommunication.

When the management device 20 receives the response to the communicationpacket 55 from the image reproduction device 10 a (“Yes” in Step S15),the management device 20 checks if the distribution of all the movingimage data 50 is finished (Step S16). When the distribution of all themoving image data 50 is not finished (“No” in Step S16), the managementdevice 20 returns the process to Step S11. On the other hand, when thedistribution of all the moving image data 50 is finished (“Yes” in StepS16), the management device 20 ends the process shown in the flowchartof FIG. 7.

When the management device 20 finds that the distribution destination ofthe moving image data 50 with the file name “fileF.mpg” is the deviceitself in Step S11, the management device 20 does not perform theprocess steps S12 to S15. The management device 20 stores the movingimage data 50 with the file name “fileF.mpg” into the storage part 17thereof.

Thus, the management device 20 distributes the moving image data 50stored in the memory card 45 by using the cascade communication which isone-to-one bidirectional communication. The management device 20 canreliably transmit the moving image data 50 to the distributiondestination and can also confirm that the distribution destination hasacquired the moving image data 50. Further, since it is not necessary toprovide the image reproduction device 10 with any interface used forupdating the moving image data 50 stored in the storage part 17, such asthe memory card slot 26, it is possible to cut the cost for the imagereproduction device 10.

The management device 20 may be provided with a general purposecommunication module (LAN module or the like), instead of the memorycard slot 26. In this case, a store salesperson may operate a PC totransmit the pieces of moving image data 50, 50, . . . , and thedistribution destination information 46 to the management device 20.

(3) Instruction for Reproduction of Moving Image Data

Next, discussion will be made on an operation flow until the managementdevice 20 and the image reproduction devices 10 start reproduction ofthe moving image data 50.

In order to reproduce the moving image data 50, the image reproductiondevices 10 and the management device 20 need to start up the decoder151. The respective starting times of the decoders 151 in the devicesare different. In order for the devices to start the reproduction of themoving image data 50 at the same time, the management device 20instructs the image reproduction devices 10 to go into a reproductionstandby state. The reproduction standby state is a state in which thedecoders 151 are up.

Specifically, the management device 20 sends a reproduction standbycommand instructing the image reproduction device 10 to go into thereproduction standby state to each of the image reproduction devices 10by cascade communication. The process for sending the reproductionstandby command is the same as that shown in the flowchart of FIG. 7. Inthe payload part 53 of the communication packet 55, stored is thereproduction standby command.

When the image reproduction device 10 receives the reproduction standbycommand, the image reproduction device 10 starts up the decoder 151thereof and goes into the reproduction standby state. The imagereproduction device 10 notifies the management device 20, by cascadecommunication, that the image reproduction device 10 has been in thereproduction standby state. The management device 20 also starts up thedecoder 151 thereof and goes into the reproduction standby state.

After confirming that all the image reproduction devices 10 have been inthe reproduction standby state, the management device 20 generates abroadcast packet 60 including a reproduction start command 61. Themanagement device 20 sends the broadcast packet 60 to all the imagereproduction devices 10 by broadcast communication at the same time.

FIG. 10 is a view showing the broadcast communication packet 60. Thebroadcast packet 60 has the same constitution as that of thecommunication packet 55 used for the cascade communication. In thedestination address part 52, however, set is “0” as an address used forthe broadcast communication. In the payload part 53, stored is thereproduction start command 61.

The image reproduction device 10, receiving the broadcast packet 60,starts the reproduction of the moving image data 50 on the basis of thereproduction start command 61. After sending the broadcast packet 60,the management device 20 starts the reproduction of the moving imagedata 50. On starting the reproduction of the moving image data 50, therespective cumulative counter parts 153 of the image reproductiondevices 10 and the management device 20 start counting the clock signal.

The timing at which all the image reproduction devices 10 receive thebroadcast packet 60 and start the reproduction of the moving image data50 is almost the same as the timing at which the management device 20starts the reproduction of the moving image data 50. Therefore, theimage reproduction devices 10 and the management device 20 start thereproduction of the moving image data 50 at the same time.

(4) Synchronized Display of Moving Image Data 50

After instructing the image reproduction devices 10 to start thereproduction, the management device 20 periodically sends thesynchronization information 252 by broadcast communication.

The panel control part 16 of the management device 20 updates the frameto be displayed on the display part 210 thereof. The synchronizationinformation transmitting part 251 records the cumulative count value ofthe cumulative counter part 153 at the timing for updating the frame, asthe reference count information 253. The synchronization informationtransmitting part 251 periodically generates the synchronizationinformation 252 including the reference count information 253 and thetime stamp indicating the last frame update time and broadcasts thegenerated synchronization information 252 to the image reproductiondevices 10.

The time interval for broadcasting the synchronization information 252is not particularly defined. It is preferable, however, that themanagement device 20 should broadcast a plurality of pieces ofsynchronization information 252 per second. Since the difference in theframe number among the image reproduction devices 10 and the managementdevice 20 can be thereby kept very small, it is possible to continuouslydisplay a unified video image on the whole of the display rack 4.

When the image reproduction device 10 receives the synchronizationinformation 252 during the reproduction of the moving image data 50, theimage reproduction device 10 adjusts the frame to be displayed on thedisplay part 110 thereof on the basis of the synchronization information252.

FIG. 11 is a flowchart showing an operation flow of the imagereproduction device 10 for adjusting the frame to be displayed on thedisplay part 110 thereof by using the synchronization information 252.The image reproduction device 10 performs an operation shown in theflowchart of FIG. 11 concurrently with the reproduction of the movingimage data 50.

When the synchronization information 252 is received (“Yes” in StepS21), the frame adjustment part 154 calculates a difference between thecount value of the reference count information 253 included in thesynchronization information 252 and the count value of the cumulativecount information 155 (Step S22).

When the difference obtained in Step S22 is not smaller than a thresholdvalue (“Yes” in Step S23), the frame adjustment part 154 rewrites thecumulative count value and the count value of the cumulative countinformation 155 by using the count value of the reference countinformation 253 (Step S24). Then, the frame adjustment part 154specifies a frame number corresponding to the rewritten count value ofthe cumulative count information 155 (Step S25).

For example, the frame number can be specified by dividing the countvalue of the cumulative count information 155 by the update count valueindicating the time interval for updating the frame. In a case where thecount value of the cumulative count information 155 is “3687” and theupdate count value is “242, the quotient is “153.625”. As a result, theframe adjustment part 154 specifies “153” as the frame number.

The frame adjustment part 154 notifies the panel control part 16 of thespecified frame number. The panel control part 16 displays a framecorresponding to the notified frame number on the display part 110 (StepS26). As a result, the frame numbers of the frames displayed on theimage reproduction devices 10 are synchronized with the frame number ofthe frame displayed on the management device 20.

The timings at which the image reproduction devices 10 receive thesynchronization information 252 are almost the same. For this reason,the adjustments of the frames to be displayed on the image reproductiondevices 10, on the basis of the synchronization information 252, areperformed at almost the same timing. As a result, the frame numbers ofthe frames displayed on the image reproduction devices 10 and themanagement device 20 are synchronized with one another. As shown in FIG.4C, it is possible to display a video image with a sense of unity on thewhole of the display rack 4.

When the difference is smaller than the threshold value in Step S23(“No” in Step S23), the frame adjustment part 154 does not notify thepanel control part 16 of the frame number. In other words, the panelcontrol part 16 displays the frame on the display part 110 in the orderof the frame number. Since whether the frame should be changed or not isdetermined on the basis of the difference, the image reproduction device10 does not need to change the frame to be displayed every time when theimage reproduction device 10 receives the synchronization information252. Therefore, it is possible to reduce the load of the imagereproduction device 10.

When the reproduction of the moving image data 50 is finished (“Yes” inStep S27), the image reproduction device 10 ends the process shown inthe flowchart of FIG. 11. Further, the image reproduction device 10 mayend the process of FIG. 11 also when the image reproduction device 10receives a reproduction end command from the management device 20.

Since the image reproduction devices 10 and the management device 20individually reproduce the moving image data 50, the display system 1does not have to distribute the frame to the image reproduction devices10 and the management device 20. Therefore, it is possible to simplifythe configuration of the display system 1 and lower the price. Further,the data size of the synchronization information 252 is much smallerthan that of the frame which is distributed by the content reproductiondevice. For this reason, since data transfer can be performed by usingRS-485 or the like with relatively low data transfer rate, it ispossible to further lower the cost.

The image reproduction device 10 continues to reproduce the moving imagedata 50 when the image reproduction device 10 does not receive thesynchronization information 252. Therefore, a video image iscontinuously displayed on the whole of the display rack 4 even when thesynchronization information 252 is not broadcasted because of abreakdown of the management device 20, or the like. Similarly, even whena situation occurs where any one of the image reproduction devices 10and the management device 20 cannot display any video image, the otherdevices continue to reproduce the moving image data 50. Thus, in thedisplay system 1, it is possible to prevent occurrence of a situationwhere no video image can be displayed on the whole of the display rack 4even when a particular device is out of order.

Further, even when a situation occurs where the synchronization of theframe numbers cannot be performed by using the synchronizationinformation 252, only if the difference in the frame number among theimage reproduction devices 10 and the management device 20 is aboutseveral frames, it is possible to maintain a video image with a sense ofunity to be displayed on the whole of the display rack 4.

Thus, in the display system 1 of the preferred embodiment, one videoimage is displayed on the whole of the display system 1 by causing theimage reproduction devices 10 and the management device 20 toindividually reproduce the moving image data 50. The management device20 distributes the moving image data 50 to the image reproductiondevices 20 by cascade communication and sends the synchronizationinformation 252 to the image reproduction devices 10 by broadcastcommunication. Since this eliminates the necessity of providing thecontent reproduction device for distributing the frames, it is possibleto simplify the configuration of the display system 1.

Though discussion has been made on the operation of rewriting thecumulative count value and the cumulative count information 155 (StepS24) when the difference is not smaller than the threshold value (“Yes”in Step S23) in the process shown in the flowchart of FIG. 11 in thepreferred embodiment, this is only one exemplary case. For example, in acase where the crystal oscillator is a PLL (Phased Locked Loop) circuit,the image reproduction devices 10 may correct the frequency of the clocksignal outputted from the PLL circuit so that the count value of thecumulative count information 155 may be coincident with the count valueof the reference count information 253.

Though discussion has been made on the case where the management device20 generates the synchronization information 252 including the referencecount information 253 in the preferred embodiment, this is only oneexemplary case. The management device 20 may generate thesynchronization information 252 by using information indicating theframe number of the frame displayed on the display part 210, instead ofthe reference count information 253.

If the format of the moving image data 50 is MPEG, the management device20 may generate the synchronization information 252 by using a value ofan STC (System Time Clock), instead of the reference count information253. In this case, the cumulative counter part 153 corresponds to theSTC. The image reproduction device 10 corrects the value of the STCthereof on the basis of the value of the STC included in thesynchronization information 252 and adjusts the timing for displayingthe frame and the timing for decoding, by using the corrected value ofthe STC. The management device 20 needs to synchronize the STCs of theimage reproduction devices 10 and the management device 20 before thereproduction of the moving image data 50 is started.

Though discussion has been made on the case where the management device20 broadcasts the synchronization information 252 in the preferredembodiment, this is only one exemplary case. When a state where thesynchronization information 252 cannot be received from the managementdevice 20 continues for a predetermined time period, any one of theimage reproduction devices 10, instead of the management device 20, maysend the synchronization information 252. For example, the imagereproduction device 10 may automatically determine whether thesynchronization information 252 should be broadcasted or not.Alternatively, the image reproduction device 10 may be provided with aswitch indicating On/Off of the function of sending the synchronizationinformation 252.

Though discussion has been made on the case where the cascadecommunication and the broadcast communication are performed by using thecommunication cable 30 in the preferred embodiment, this is only oneexemplary case. As shown in FIG. 12, the display system 1 may comprisecommunication cables 31, 31, . . . for cascade communication. In thiscase, the communication cable 30 is used for broadcast communication.Since the management device 20 does not need to perform time sharingmanagement for the cascade communication and the broadcastcommunication, it is possible to reduce the load of the managementdevice 20.

One of the communication cables 31 for cascade communication connectsthe management device 20 and the image reproduction device 10 a to eachother. Another one of the communication cables 31 connects the imagereproduction device 10 a and the image reproduction device 10 b to eachother. Still another one of the communication cables 31 connects theimage reproduction device 10 b and the image reproduction device 10 c toeach other. Still another one of the communication cables 31 connectsthe image reproduction device 10 c and the image reproduction device 10d to each other. Yet another one of the communication cables 31 connectsthe image reproduction device 10 d and the image reproduction device 10e to each other.

When the cascade communication is used for transmission, the managementdevice 20 transmits the communication packet 55 to the imagereproduction device 10 a via the communication cable 31. When thedistribution destination of the received communication packet 55 is notthis device, the image reproduction device 10 a transmits thecommunication packet 55 to the image reproduction device 10 b via thecommunication cable 31. Thus, when the image reproduction device 10receives the communication packet 55 whose destination is not thisdevice, the image reproduction device 10 transmits the communicationpacket 55 to the next image reproduction device 10. When the imagereproduction device 10 receives the communication packet 55 whosedestination is this device, the image reproduction device 10 performsreception of the communication packet 55.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A display system, including: a first image reproduction device (10)for reproducing first moving image data (50); and a second imagereproduction device (20) for reproducing second moving image data (50),which can be communicated with said first image reproduction device,wherein said first image reproduction device (10) and said second imagereproduction device (20) each comprise: a storage part (17) for storingtherein moving image data to be reproduced by said device itself; adecoder (151) for decoding said moving image data stored in said storagepart, to thereby generate a frame; and a display part (110, 210) fordisplaying said frame thereon in the order of frame number, wherein saidsecond image reproduction device (20) further comprises: asynchronization information transmitting part (251) for transmittingsynchronization information including information specifying a framenumber of a reference frame displayed on said display part (210) of saidsecond image reproduction device (20) to said first image reproductiondevice by unidirectional communication, and wherein said first imagereproduction device (10) further comprises: a frame adjustment part(154) for specifying said frame number of said reference frame on thebasis of said synchronization information and displaying a framecorresponding to said frame number specified thus on said display part.2. The display system according to claim 1, further including: a thirdimage reproduction device (10) for reproducing third moving image data(50), wherein said synchronization information transmitting part (251)includes: a broadcast communication part (18) for broadcasting saidsynchronization information to said first image reproduction device (10)and said third image reproduction device (10) by unidirectionalcommunication.
 3. The display system according to claim 1, wherein saidfirst moving image data (50) and said second moving image data (50) arepieces of divided moving image data (500) into which one moving imagedata is divided, being different from each other.
 4. The display systemaccording to claim 1, wherein said information specifying said framenumber is a frame number of said reference frame.
 5. The display systemaccording to claim 1, wherein said second image reproduction device (20)further comprises: a first clock generation part(152) for generating afirst clock signal; and a first counter part (153) for counting saidfirst clock signal from the time when reproduction of said second movingimage data is started, and wherein said information specifying saidframe number is a count value of said first clock signal correspondingto a timing at which said reference frame is displayed on said displaypart of said second image reproduction device, and said frame adjustmentpart (154) specifies said frame number of said reference frame from saidcount value of said first clock signal which is included in saidsynchronization information.
 6. The display system according to claim 5,wherein said first image reproduction device (10) further comprises: asecond clock generation part (152) for generating a second clock signal;and a second counter part (153) for counting said second clock signalfrom the time when reproduction of said first moving image data isstarted, and wherein said frame adjustment part (154) displays a framecorresponding to said frame number specified thus on said display part(110) when a difference between a count value of said second clocksignal and said count value of said first clock signal which is includedin said synchronization information is not smaller than a predeterminedvalue.
 7. The display system according to claim 2, wherein said firstimage reproduction device (10) further comprises: an alternativesynchronization information transmitting part (15) for generatingalternative synchronization information including information specifyinga frame number of a frame displayed on said display part of said devicewhen said synchronization information cannot be received for apredetermined time period and transmitting said alternativesynchronization information to said third image reproduction device byunidirectional communication.
 8. The display system according to claim1, wherein said second image reproduction device (20) further comprises:an individual communication part (18) for instructing said first imagereproduction device (10) to go into a reproduction standby state inwhich said first moving image data (50) can be reproduced, by one-to-onecommunication; a transition part (25) for bringing said decoder and saiddisplay part (16, 21) of said device into a state in which said secondmoving image data (50) can be reproduced; and a reproduction instructionpart (25) for instructing said first image reproduction device (10) tostart reproduction of said first moving image data (50) byunidirectional communication and instructing said decoder (151) and saiddisplay part (210) of said device to start reproduction of said secondmoving image data (50), when information indicating that said firstimage reproduction device (10) has been in a reproduction standby stateis received from said first image reproduction device (10).
 9. Thedisplay system according to claim 1, wherein said second imagereproduction device (20) further comprises: an input part (26) forinputting a plurality of pieces of inputted moving image data anddistribution destination information indicating a distributiondestination of each inputted moving image data from the outside; and adistribution part (18) for storing said inputted moving image data forsaid device into said storage part and distributing said inputted movingimage data for said first image reproduction device to said first imagereproduction device by one-to-one communication, on the basis of saiddistribution destination information.
 10. An image reproduction device(20) connected to a first display device (10) for displaying firstmoving image data thereon, comprising: a storage part (17) for storingsecond moving image data (50) therein; a decoder (151) for decoding saidsecond moving image data (50) stored in said storage part, to therebygenerate a frame; a display part (210) for displaying said frame thereonin the order of frame number; and a synchronization informationtransmitting part (251) for transmitting synchronization informationincluding information specifying a frame number of a frame displayed onsaid display part (210) to said first display device by unidirectionalcommunication.
 11. The image reproduction device (20) according to claim10, wherein said synchronization information transmitting part (251)includes: a broadcast communication part (18) for broadcasting saidsynchronization information to said first display device (10) and asecond display device (10) when said device is connected to said seconddisplay device (10) for displaying third moving image data (50) thereon.12. An image reproduction device (10) connected to a display device (20)for displaying first moving image data (50) thereon, comprising: astorage part for storing second moving image data (50) therein; adecoder (151) for decoding said second moving image data (50) stored insaid storage part, to thereby generate a frame; a display part (110) fordisplaying said frame thereon in the order of frame number; and a frameadjustment part (154) for specifying a frame number of a reference framedisplayed on said display device (20) on the basis of synchronizationinformation when said synchronization information including informationspecifying said frame number of said reference frame is received anddisplaying a frame corresponding to said frame number specified thus onsaid display part.